<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<div id="app">
  下拉框:
    <select v-model="checked">
        <option>A</option>
        <option>B</option>
        <option>C</option>
    </select>
    <span>{{checked}}</span>
</div>

<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
    var vm = new Vue({
        el: '#app',
        data:{
            checked:''
        }
    })

</script>
</body>
</html>